iwlwifi: mvm: free RX reorder buffer on restart

Restart flow zeroes the rx_ba_sessions counter. Mac80211 asks
driver to tear down of the session only afterwards, and as a
result driver didn't free the data. Fix it.

Signed-off-by: Sara Sharon <sara.sharon@intel.com>
Fixes: 10b2b201

 ("iwlwifi: mvm: add infrastructure for tracking BA session in driver")
Signed-off-by: Luca Coelho <luciano.coelho@intel.com>